BI 655066 (Risankizumab) Compared to Placebo and Active Comparator (Ustekinumab) in Patients With Moderate to Severe Chronic Plaque Psoriasis

* Male or female patients with age ≥18 years at screening. * Have a diagnosis of chronic plaque psoriasis (with or without psoriatic arthritis) for at least 6 months before the first administration of study drug. * Have stable moderate to severe chronic plaque psoriasis with or without psoriatic arthritis at both Screening and Baseline (Randomisation): 1. Have an involved body surface area (BSA) ≥10% and 2. Have a Psoriasis Area and Severity Index (PASI) score ≥12 and 3. Have a static Physician Global Assessment (sPGA) score of ≥3. * Must be candidates for systemic therapy or phototherapy for psoriasis treatment, as assessed by the investigator. * Must be a candidate for treatment with Stelara® (ustekinumab) according to local label.

* Patients with: 1. non-plaque forms of psoriasis (including guttate, erythrodermic, or pustular) 2. current drug-induced psoriasis (including an exacerbation of psoriasis from beta blockers, calcium channel blockers, or lithium) 3. active ongoing inflammatory diseases other than psoriasis and psoriatic arthritis that might confound trial evaluations according to investigator's judgment * Previous exposure to BI 655066. * Previous exposure to ustekinumab (Stelara®).